The present invention relates to a solid fuel pulverizer and exhauster system which is suitable for use in association with a fossil fuel-fired steam generator in a new utility unit application or a retrofit application in an existing utility unit.
Pulverizers are well known for the reduction of the particle size of solid fuel to allow for combustion of the solid fuel in a furnace. A pulverizer employs some combination of impact, attrition and crushing to reduce a solid fuel to a particular particle size. Several types of pulverizer mills can be employed for the pulverization of the solid fuel, for example, coal, to a particulate size appropriate for firing in a furnace. These can include ball-tube mills, impact mills, attrition mills, ball race mills, and ring roll or bowl mills. Most typically, however, bowl mills with integral classification equipment are employed for the pulverization of the solid fuel to allow for transport, drying, and direct firing of the pulverized fuel entrained in an air stream.
Bowl mills have a grinding ring carried by a rotating bowl. Fixed position rollers are mounted on roller journal assemblies such that the roll face of the rollers are approximately parallel to the inside surface of the grinding ring and define a very small gap therebetween. Pressure for grinding is applied through springs or hydraulic cylinders on the roller journal to crush solid fuel caught between the roll face of the roller and the grinding ring.
An air stream is typically utilized for drying, classification, and transport of the solid fuel through the pulverizer. The air stream employed is typically a portion of the combustion air referred to as the primary air. The primary air is combustion air first directed through a preheater whereby the combustion air is heated with energy recovered from the flue gas of the furnace. A portion of the primary air is then ducted to the pulverizers. In a bowl mill, the primary air is drawn through beneath the bowl of the bowl mill and up past the roller journal assemblies to collect the pulverized solid fuel. The small particles of solid fuel become entrained in the primary air. The air stream containing the solid fuel then passes through a classifier into the outlet of the pulverizer. After passing through the exhauster, the pulverized fuel can be stored, or more typically, is transported to the furnace by the air stream for direct firing.
A fan assembly, referred to as an exhauster, is used to pump the air stream through the pulverizer. The exhauster is conventionally positioned on the outfeed side of the pulverizer for drawing the primary air through the pulverizer. This arrangement of pulverizer and exhauster is referred to as a suction system. The capacity of a pulverizer is a function of the solid fuel properties, pulverizer size, and air flow through the pulverizer. In a suction system, where the exhauster induces air flow through the pulverizer, improvement of the performance of the exhauster will in some cases result in improvement in the performance of the pulverizer. In a suction system wherein an exhauster is positioned on the outfeed side of a bowl mill, the air stream outlet of the bowl mill is typically at an elevated position relative to the inlet of the exhauster. A duct directs the air stream of primary air and pulverized fuel from the outlet of the bowl mill downward and generally through an elbow in the duct of greater than (90) ninety degree angle into the inlet of the exhauster.
In the United States of America, federally mandated emissions limits and increased competitive pressures have motivated utility unit operators to change their existing coal supplies such that those types of coal which a particular utility unit had originally been designed to handle are now mixed with other types of coal or replaced completely by other types of coal. For example, some utility unit operators are contemplating switching to a rank of coal which has a relatively higher moisture, relatively lower heating content, and a relatively lower sulfur than the original design basis coal or mixing such different coal with the original design basis coal. However, such utility unit operators face the reality that the pulverized solid fuel feed components of their utility units, which comprise at least one pulverizer for pulverizing the coal and its associated air transport components such as an exhauster fan, are not capable of reliably performing the grinding and transport of such substitute coal or substitute coal and original design coal mixtures. In some instances, the existing pulverizers and their associated air transport components do not have, or cannot be adjusted to provide, the increased throughput required for the use of such substitute coal or substitute coal mixtures.
The need thus exists for a solid fuel pulverizer and exhauster system which can reliably handle, in cooperation with other components, the solid fossil fuel grinding and air transport requirements of existing utility units which a utility unit operator desires to retrofit so as handle such relatively higher moisture, relatively lower heating content, and a relatively lower sulfur coal.
To thus summarize, a need has been evidenced in the prior art for a solid fuel pulverizer and exhauster system that would be particularly suited for use in effecting the pulverization of material such as, for example, coal.
It is, therefore, an object of the present invention to provide a new and improved solid fuel pulverizer and exhauster system for effecting the pulverization of material such as, for example, coal.
Yet another object of the present invention is to provide such a solid fuel pulverizer and exhauster system which is capable of being retrofitted in connection with existing bowl mills.
In accordance with one aspect of the present invention, these and other objects of the present invention are achieved by a method for retrofitting a solid fuel pulverizer and exhauster system including at least one pulverizer acting in cooperative association with a fuel-fired steam generating power plant which includes a furnace, the at least one pulverizer operative for pulverizing material into smaller particles, the pulverizer including a rotating vertical spindle supported therewithin, a grinding table supported on the vertical spindle for rotation thereby, at least one grinding roll operable to exert a grinding force on material disposed on the grinding table for effecting the pulverization thereof, a bowl drive means for rotating the vertical spindle, a mill gear set for operably interconnecting the vertical spindle and the bowl drive means, and classifier means for classifying the pulverized solid fuel between a discharge condition in which some of the pulverized solid fuel is suitable for discharge from the at least one pulverizer to the furnace and a non-discharge condition in which the remaining pulverized solid fuel is retained in the at least one pulverizer for further pulverizing, an exhauster assembly having an exhauster housing defining an inlet opening and a fan rotatably mounted in the exhauster housing, the fan providing an air stream, fan drive means for drivingly rotating the fan, and an exhauster fan coupling for operably interconnecting the fan and the fan drive means taken from the bowl drive motor and gear train and a duct interconnecting the exhauster assembly and the furnace for the feed of pulverized solid fuel therealong from the exhauster assembly to the furnace. In accordance with the one aspect of the present invention, the method includes replacing the bowl drive motor with a new drive motor which is operable to drivingly rotate the bowl at the pre-retrofit speed but which provides relatively more horsepower than the replaced bowl drive motor and replacing the original exhauster fan drive coupling with a new exhauster fan gear set which effects rotation of the exhauster fan at a relatively higher rotational speed than the pre-retrofit speed and can be driven by a separate drive motor of a single operating speed or arranged with a variable speed controller.
In accordance with another aspect of the present invention, the objects of the present invention are achieved by a method for retrofitting a solid fuel pulverizer and exhauster system including at least one pulverizer acting in cooperative association with a fuel-fired steam generating power plant which includes a furnace, the at least one pulverizer operative for pulverizing material into smaller particles, the pulverizer including a rotating vertical spindle supported therewithin, a grinding table supported on the vertical spindle for rotation thereby, at least one grinding roll operable to exert a grinding force on material disposed on the grinding table for effecting the pulverization thereof, a bowl drive means for drivingly rotating the vertical spindle, a mill gear set for operably interconnecting the vertical spindle and the bowl drive means, and classifier means for classifying the pulverized solid fuel between a discharge condition in which some of the pulverized solid fuel is suitable for discharge from the at least one pulverizer to the furnace and a non-discharge condition in which the remaining pulverized solid fuel is retained in the at least one pulverizer for further pulverizing, an exhauster assembly having an exhauster housing defining an inlet opening and a fan rotatably mounted in the exhauster housing, the fan providing an air stream, fan drive means for drivingly rotating the fan, an exhauster fan gear set for operably interconnecting the fan and the fan drive means, and a duct interconnecting the exhauster assembly and the furnace for the feed of pulverized solid fuel therealong from the exhauster assembly to the furnace. In accordance with this other aspect of the present invention, the method includes replacing the original bowl drive motor with a new drive motor which is operable to drivingly rotate the input drive gear at a speed higher than the pre-retrofit speed and which provides relatively more horsepower than the replaced bowl drive motor, replacing the original mill gear set with a new mill gear set operable to rotate the bowl at the original rotational speed while the input gear rotates at a relatively higher speed. With this arrangement, the exhauster drive motivation is taken from a direct coupling to the bowl drive input gear which effects rotation of the exhauster fan at a relatively higher rotational speed than the pre-retrofit speed.
In accordance with a further aspect of the present invention, the objects of the present invention are achieved by a solid fuel pulverizer and exhauster system acting in cooperative association with a fuel-fired steam generating power plant which includes a furnace. The solid fuel pulverizer and exhauster system includes at least one pulverizer operative for pulverizing material into smaller particles, the pulverizer including a rotating vertical spindle supported therewithin, a grinding table supported on the vertical spindle for rotation thereby, at least one grinding roll operable to exert a grinding force on material disposed on the grinding table for effecting the pulverization thereof, a bowl drive means for drivingly rotating the vertical spindle, a mill gear set for operably interconnecting the vertical spindle and the bowl drive means, and classifier means for classifying the pulverized solid fuel between a discharge condition in which some of the pulverized solid fuel is suitable for discharge from the at least one pulverizer to the furnace and a non-discharge condition in which the remaining pulverized solid fuel is retained in the at least one pulverizer for further pulverizing. The solid fuel pulverizer and exhauster system also includes an exhauster assembly having an exhauster housing defining an inlet opening and a fan, rotatably mounted in the exhauster housing, the fan providing an air stream, an exhauster fan drive motor having a drive shaft, the exhauster fan drive motor for drivingly rotating the fan, and an exhauster fan transmission assembly for operably interconnecting the fan and the exhauster fan drive motor, the exhauster fan transmission assembly being operable to translate the rotation of the drive shaft of the exhauster fan drive motor through ninety (90) degrees to thereby effect rotation of the fan by the exhauster fan drive motor of a single speed or which may be arranged with a variable speed control and soft start capability. The solid fuel pulverizer and exhauster system also includes and a duct interconnecting the exhauster assembly and the furnace for the feed of pulverized solid fuel therealong from the exhauster assembly to the furnace.
Other objects of the invention will become apparent from review of the specification and drawings.